The Best Lighting for Perfect Chroma Key Effects
Chroma key effects are a great way to allow your movies to enter worlds that you can't really shoot in. Whether it's space or a place that's over 1000 miles away, a great chroma key effect will sell the idea that you're really there to the audience. But, if you're going to pull off this effect convincingly, then you need to have the right lighting.
Lighting for chroma key is done in two parts. Part one deals with lighting the green (or blue) screen properly and part two deals with lighting the subjects.
Lighting the Green Screen
Chroma key works by isolating one specific color and then turning it transparent in post production. This color is either green or blue. Green is used more than blue because it's a color that isn't very common in props or clothing. It should also be mentioned that you should never have actors wearing colors similar to the ones that will be keyed out. Otherwise, you're going to have transparent video where their clothes were.
Your goal for lighting the green screen is to keep it as evenly lit and uniform as possible. You want the editor to just have to key out one specific color for the effect to be it's best. Otherwise, he will have to key out up to 10 shades of green and could end up intruding on the subject.
How you light the screen is largely dependent on where it is. If you're in a studio, then the best place for your lights is up on the grid shining down. Cyc lights are specifically designed for creating even lighting this way because of a special reflector built inside them. If you're on location and have to build your green screen, then a couple of bright lights off to the side will do the trick. Just remember to make every inch of the screen evenly exposed. You should also flag off these lights to prevent them from spilling on your subject.
Lighting the Subject
Lighting the subject can get a little more trickier. You need to study the lighting for the video that will be replacing the green screen and match your lighting to it. If the key light is coming from the right in the video, then you need to set your key light on the right. The lighting must match so that it looks like the subject was really there. And, when you set up these lights, you need to be very careful not to let any of it spill on to the green screen. If that happens, then set a flag to kill that excess light, otherwise you're going to be pulling your hair out during the edit.